There are many designs of electrical plug outlets or receptacles for receiving a blade type electrical plug connector. A common example of this type of device is the wall outlet found in any home and used to furnish a simple and convenient connection for an electrical appliance or the like. In many receptacles, the blades of the plug make connection upon insertion by spreading the spring clip jaws of the electricl connector. The spring tension of the electrical connector itself provides the contact pressure for maintaining the blade in sufficient contact therewith to ensure a good, safe electrical connection. However, as the spring clip jaws of the female connector providing the spring tension form part of the current path through the receptacle, they are subject to heating and constant flexing through insertion and removal of the plug. This has a tendency to diminish the spring tension and hence the contact pressure as the receptacle is used. As the contact pressure diminishes, the resistance between the blade and the connector increases which further increases the heating and loss of spring tension in the connection.
In low voltage applications, it is even more important to have good contact pressure as a small voltage drop can interfere with circuit operation. For instance, in a 12 volt circuit, a loss of 2 or 3 volts can seriously affect the operation of a battery charger which must generally maintain an applied voltage higher than the rated battery voltage during charging. Thus, it becomes increasingly important to ensure a relatively higher level of contact pressure and if possible to isolate the current carrying members of the connector from the portion of the connector providing the contact pressure. Also, in lower voltage applications, it is desirable to provide a "wiping" action as the plug is inserted in the receptacle. This helps clean the contact surfaces upon each insertion and removal to ensure a good electrical connection therebetween. Still another desirable feature of a low voltage receptacle and plug-in connector is that the blades be self seating within the receptacle. It would be undesirable from an operational standpoint to require that the plug to be precisely inserted in a certain orientation or manner other than to the extent required to align the blades with the holes in the receptacle. Any human operator of the device would expect this from his common ordinary experience, and a good design should accommodate this expectation.
It is also desirable in many applications to disconnect or connect a separate circuit if a plug is inserted into the receptable. For instance in a battery charging circuit it is desirable to disable the operation of the device upon insertion of a plug providing power to the batteries contained within the device. This would prevent a machine operator from attempting to operate the machine while the battery charger is connected.
Another requirement of a receptacle of this nature is that it be relatively low cost and, if possible, capable of being manufactured through low cost methods such as injection molding. Once manufactured, any assembly should be kept to a minimum, with the possible exception of having the capability of renewing the electrical contact surfaces of the receptacle in a convenient manner.
A receptacle providing the many advantages and benefits described above has been invented as is disclosed and claimed herein. The receptacle includes a face having a pair of blade openings canted for a standard D-C plug-in and arranged for flush mounting. A back body member may be integrally molded with the face and has slots for the installation of bracket-type terminals. A contact pressure element is generally wedge shaped, is spring loaded from the back body member, and has flattened surfaces which rest against the terminals. The body member has a center guide platform extending between the blade openings, the contact pressure element having a center guide notch to match and line up with the guide platform and ride therealong as the blades of a plug are inserted through the blade openings. This helps to center the blades upon insertion. A push button snap switch is mounted beneath the contact pressure element with its push button operator aligned with the post extending through the contact pressure element and the back body such that as the blades are inserted into the receptacle, they push against the flattened surfaces of the contact pressure element and bring the head of the post against the push button operator to actuate the snap switch. The pressure of the spring can be adjusted to vary the contact pressure between the blade and the terminal, and also provides the wiping action as the blade is inserted.
Thus, the receptacle of the present invention provides a high contact pressure especially suited for low voltage applications with a wiping action between the blades and terminals during each insertion or removal thereof, and which isolates the spring member from the electrical circuit such that the tension of the spring is not affected through heating. The novel contact pressure element serves the dual purpose of providing a self centering surface which forces the blades against the terminals, and which carries the post or stem member of the spring loaded mechanism against the push button snap switch to actuate same as the blades of the plug are inserted or removed. These and other beneficial features of the invention are more fully explained in the drawings and the following description of the preferred embodiment.